"Your image is everything," said Thibodeaux, 25, who graduated from the University of Houston in May and recently landed her first job as a TV production assistant.

"What you wear shows whether you take yourself seriously. If you look professional, it shows you care about yourself and will care about your job. It shows you're ready to work."

Although she's young, Thibodeaux said she understands there are rules for office dress, whether defined or not.

But for every recent college graduate who knows what to wear to the office, there are many more who don't.

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They sashay into job interviews or their first day at work wearing flips-flops, miniskirts or rompers. They expose tattoos, reveal cleavage or show off legs in short skirts and 5-inch platform heels.

"When you wear something inappropriate or too casual, it signals you don't care about your job," said Diane Gottsman, a nationally recognized etiquette expert and owner of the Protocol School of Texas in San Antonio. "You need to show you're clean, professional and respectful of your job, your boss and your colleagues. If you have an attitude that you don't care or you're entitled to dress the way you want, you won't get very far," she said.

It's a hard sell to a social-media generation that's constantly bombarded with Snooki-esque images of young women in clubwear and guys in tattered jeans and flip-flops. It's also a hurdle to persuade college graduates to dress in tailored, more conservative attire when there seems to be much ambiguity about what's considered professional.

"Sometimes, young people don't have the experience to know better," said Jamie Belinne, assistant dean for Career Services at the C.T. Bauer College of Business at the University of Houston. "But they should know better. When your dress is distracting from your performance, it affects your image.

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"They are getting mixed messages all the time," Belinne said. "Every company defines what's office appropriate or business casual differently. But the definition of 'business dress' is a suit. Business casual is one step down from that."

UH Bauer College of Business has instituted a Dress for Success program to educate students on image development and professional style. When in doubt, college graduates are advised to follow the lead of the company's senior management.

"It sounds cliché, but you dress for the job you want, not the job you have," Belinne said. "If you think you look cute or sexy, or if it's something you would wear on the weekend, you should change clothes immediately."

"I despise them because you can't list everything," she said. "It's much harder for women because we have so many choices."

Rapp said she's had many spirited conversations with human-resources professionals about dress codes. She expects her clients to interview in business attire: men in a suit, women in slacks and jacket or skirt and a jacket.

"As you start a new job, you need to establish credibility. The first impression is by your appearance. Don't blow it right out of the gate, even if it's in style. Be smart."

Jessica Quirk, author of "What I Wore: Four Seasons, One Closet, Endless Recipes for Personal Style" (Ballantine Books, $18), said college students aren't getting the guidance they need to make decisions about what's appropriate.

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WHAT NOT TO WEAR

Midriff tops or low-rise pants

Too much cleavage or anything too tight

Miniskirts. (A good rule is stick with hems no more than 2 inches above the knee.)

"Everyone used to know the rules, but workplaces have become so casual," she said. "It's easy to be overtly sexy without even thinking about it, but it's a mistake. You should look polished and put together."

Quirk, now 28, had to adjust her wardrobe when she moved to New York after graduating from the University of Indiana in Bloomington. Although she landed a job in the creative fashion arena, she wanted to look professional without standing out. She learned to shop vintage and thrift stores to find unique pieces that gave her a creative look without being too casual.

Quirk became so adept at putting her outfits together that she started a blog, What I Wore, to chronicle her daily transformations.

"You have to be open to learning the job and how to dress for the job," she said.

Some companies are ditching the "business casual" dress code for more formal look, said personal and corporate image consultant Helen Perry.

"They've realized business casual has been abused, and it doesn't work in maintaining a company's image," she said. "The more sophisticated offices are going back to suits and business professional attire."

Perry advises tailored slacks, jackets, blouses, comfortable and well-polished shoes. She said women have more ways to sabotage their credibility with their dress because they have more options. But jackets always bring more credibility, she said.

"It doesn't mean you have to wear a suit and pantyhose, but you want to look classic," she said.

"You also don't want to look one way one day and another the next. You have to be consistent about your look. After all, it's your brand."